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site-built, mobile/manufactured and modular homes

What is causing soft spots in my mobile/manufactured home floor?

Thursday, November 4, 2021

Soft spots in a mobile home floor are always caused by an area of long-term or repeated wetness, and it can come from above, below, or the side:

ABOVE - A poorly installed marriage line connection at the ridge line of a double-wide can allow a gap to open up and water to run down, sometimes along the roof framing, before it drops elsewhere to the floor. Ordinary roof leaks can also do it. Splashed water around a shower or tub, if done repeatedly and allowed to sit, is another culprit. Or the spilled water around pet food bowls.

BELOW - Leaking plumbing will drip into puddles on the belly board, creating a bulge, wet areas, and high humidity below the floor. Also, an oversize air conditioner can cause condensation on the wood subfloor. When the a/c unit is rated for significantly more BTUs than what is recommended by the manufacturer, the system will cool the home too quickly, not allowing the necessary air flow time over the evaporator coils to provide adequate dehumidification. Combine that with a thermostat set in the lower 70s, and condensation will wet the surface of the floor where the cold above and warm air below meet. Even worse, close a floor supply register, which pressurizes the connection of the duct to the register above, and see what the leaked cold air gushing into the enclosed floor structure voids will do.

    A mobile home we inspected last month had a 5-ton package air conditioner connected to a double-wide rated by the manufacturer for a max 2.5 ton unit. Plus, the home was sited on continuously moist soil at the edge of a Florida swamp, and had large tears in the belly board. Then, to top it off, the homeowner had replaced his water heater at the inside laundry room with one of those new heat-pump units. It exhausts additional cold air into the home as part of heating the water. Condensation soft spots in the floor were everywhere, some with temporary patches nailed over them. Most of the floor, walls and ceiling in the area around the new water heater had been torn out, with mold showing on parts of the drywall that remained.

THE SIDE - Mobile homes are notorious for leaking rainwater at the bottom corner of windows. It runs down to the floor level and then spreads sideways, leaving a stain on the baseboard over time, and creating soft spots near the wall.

    Particle board used in older manufactured homes is more susceptible to weakening from wetness than products like plywood and OSB, but all of them are eventually damaged by high moisture. The solution, of course, is to cut out and replace the bad areas after fixing the cause of the problem.  But avoid making small repairs. The repair piece should go across at least two floor joist bays.

    To learn more about other ways mosture can attack a mobile home, and there are plenty more, download HUD’s guide “Moisture Problems in Manufactured Homes, Understanding Their Causes and Finding Solutions”. Also see What causes a crowned floor in a mobile/manufactured home? and What are the signs that a mobile home is not level?

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Here’s links to a collection of our blog posts about MOBILE/MANUFACTURED HOMES:

Where can I file a complaint if I have problems with my new or used manufactured/mobile home in Florida?

 What are the most common defects in mobile/manufactured home foundation piers? 

• • • • • • • • • • • • • • • • • • • • • • 

Want to learn more about inspecting
manufactured/mobile homes? 
Get our  Handbook for 
Manufactured Home Inspectors 
at for $19.95

• • • • • • • • • • • • • • • • • • • • • • 

How do I determine the age of a very old mobile home?

What is a "HUD label verification letter" for a mobile/manufactured home?  

When did a ground cover vapor barrier (plastic sheet) become required under a mobile/manufactured home? 

Is it safe to go under a mobile home? 

Are older mobile homes unsafe? 

What do I need to know about buying a foreclosed mobile home? 

Does it make sense to buy an older mobile home and remodel it? 

Where do I find the vehicle identification number (VIN) on a mobile home? 

How do I find out how old a mobile home is and who manufactured it?

What is the right price for a used mobile home?

How energy efficient is a mobile home?

When were the first double-wide mobile homes manufactured?

How do I upgrade my old (pre-1976) mobile home to meet HUD standards?

What size air conditioner is right for my mobile home? 

Can you move an older mobile home in Florida? 

What does the HUD tag look like and where do I find it on a mobile home? 

Can you put a zone 1 mobile home in Florida?

How can I remove water under my mobile home?

What's the differences between a trailer, a mobile home, a manufactured home, and a modular home? 

What is a D-sticker mobile home? 

What are the tie-down requirements for a mobile home?

How fireproof is a mobile home?  

Can I install a mobile home myself?

What is a Park Model mobile home?  

Does an addition to a mobile home have to comply with the HUD Code? 

What walls can I remove in a mobile home?

What can I do to prevent dampness and mold in my mobile home? 

How can I tell if a mobile home is well constructed?

How can I tell the difference between a manufactured home and a modular home?

       Visit our MOBILE/MANUFACTURED HOMES  page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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